Orthodontic procedures almost always employ a plurality of orthodontic brackets that are attached to respective teeth, usually by cementing them thereto, although in some circumstances the bracket may still be attached to a metal band which embraces the tooth. Each bracket has a mesial distal extending slot therein, usually of rectangular cross section in a gingival occlusal plane, and the brackets are connected together using an arch wire, so called because it is preformed to an optimum arch shape corresponding to the desired conformation of the teeth at the conclusion of the procedure. In the so-called labial procedures, which are the most commonly employed, the brackets are attached to the labial surfaces of the teeth and the slots open toward the labial for insertion and removal of the wire, which is retained in the slots by ligating means of some kind. In “lingual” procedures, which have the advantage that the brackets and the wire are usually concealed from frontal view, the brackets are attached to the lingual teeth surfaces and the slots open toward the lingual or occlusal. Arch wires of progressively increasing stiffness and, depending on the type of tooth movement to be achieved, also of different cross sections, are used one at a time. Historically, when first employed the brackets were “passive”, in that ligation of the arch wire to the bracket to obtain the necessary action between them was external to the bracket, at first consisting of a soft metal wire twisted around them, while increasingly an elastomeric hoop or loop is used in place of wire.
The ends of the arch wire may be engaged in terminal tubes, usually attached to the molars so as to anchor the arch wire firmly in place. Tubes may also be employed on intermediate teeth in place of brackets whenever this is appropriate. In its simplest form a terminal or intermediate tube is passive and consists of a short piece of tube attached to a base by which it is mounted on the tooth surface, the tube bore opening at least mesially so that the arch wire end must be inserted therein. This is not always convenient, and may not be possible when the tube is on an intermediate tooth, and the solution is then to use a tube of the so-called convertible type, with which one side of the tube bore can be opened when required for insertion of the wire therein, or its removal. It is also possible to incorporate in such a tube an arch wire engaging attitude controlling spring member that will urge the wire into contact with two of the slot walls, whereupon the tube is active as well as convertible. It will be apparent from the foregoing brief description that there can be considerable overlap between the function and appearance of brackets and tubes, with the result that it may be possible for a particular orthodontic device to be considered by some orthodontists as a bracket, while others will think of it as a tube. In general, a device in which its body is noticeably bigger in gingival-occlusal dimension than mesially-distally will usually be regarded by most practitioners as a bracket, while one in which the opposite is the case will be regarded as a tube.
The term “orthodontic devices” as used herein, in both the specific description and in the claims, is intended therefore to include both brackets and convertible tubes within its scope. The adjective “buccal” commonly is used to indicate that a device is on teeth that are facing the cheeks, while “palatal” or “lingual” are used to indicate that a device is facing the palate and the tongue. More specifically palatal is used in referring to the “inward” facing surfaces of the upper bicuspids and molars, but increasingly lingual is used for all teeth, while labial is used to refer to the upper and lower canines and incisors, and buccal is used to refer to the upper and lower bicuspids and molars.
Brackets as used in the Hanson SPEED System (Trade Mark) are “active”, sometimes referred to as “self-ligating”, in that each comprises a permanent ligating spring member which embraces the bracket body and is moved thereon between slot open and slot closed positions, the spring member performing the dual functions of retaining the arch wire in the slot, and also urging it to an optimum position within the slot. Specific examples of such active brackets are disclosed and claimed in my U.S. Pat. Nos. 4,248,588 and 4,492,573.
In another line of development the orthodontic device is provided with a shutter which is movable between slot open and closed positions, in slot closed position retaining the arch wire in the slot. The shutter also functions, at least initially, by its engagement with the wire to urge the device and the arch wire to their optimum or neutral position relative to one another, at which position the constraint between them is minimized. Since in at least the initial stages of the procedure the arch wire will usually be of cross section smaller than the slot, such a device preferably is provided with an internal attitude controlling spring that protrudes into the slot to engage the wire and provide a desired controlling force. Such a shutter can be of thicker material than an embracing ligating spring so that it is relatively rigid and less flexible. It can therefore more easily be made much less sensitive to overstressing beyond the elastic limit of the material, while still being sufficiently flexible for it to be held securely in slot closed position by its jamming engagement with the device body while under the onerous conditions encountered in patients' mouths during typical orthodontic procedures. Examples of devices consisting of such brackets and convertible tubes are described and claimed in my U.S. Pat. No. 6,506,049, issued 14 Jan., 2003, the disclosure of which is incorporated herein by this reference.
There is a constant endeavor to provide devices that are as small and with as smooth an exterior as possible, for cosmetic reasons to please the patient, in order to reduce as much as possible any rough contact between the tongue, the devices and the adjacent mouth tissue with its consequent discomfort, and for hygienic reasons to reduce the number of areas in which food and dental plaque can accumulate. It is of interest to both orthodontists and patients to provide devices that interfere as little as possible with speech. The orthodontist is interested in addition to use devices that while low in cost provide fast, precise and effective movement and attitude control of the teeth.
There is increasing interest in the lingual technique, even though such procedures are more difficult to implement. A compromise is to use the lingual technique only for the upper arch, where the brackets and arch wire would otherwise be most visible, and the labial technique for the lower arch, where the brackets and arch wire are mostly hidden by the lower lip. Lingual and mixed lingual/labial procedures are of special interest to adult patients who are more concerned than children with appearance during the two to three year period required for a typical procedure. The compromise is not so suitable for older patients who tend to show their lower teeth more, and in some cases primarily display their lower anterior teeth. Small smooth devices are needed particularly for the lingual location because of ready access by the tongue, and the natural tendency for the tongue to explore any foreign object in the mouth. Attempts simply to reduce the size of existing devices are not generally successful, at least partly because changes in scale affects size parameters in different ratios, e.g. areas decrease in square ratio while volumes decrease in cube ratio, with the result that it becomes increasingly difficult, especially with the tiny spring members required, to find materials of the necessary properties. Examples of such small, smooth exterior brackets suitable for lingual procedures are those described and claimed in my U.S. Pat. Nos. 4,698,017 and 5,685,711, issued respectively 06 Oct. 1987 and 11 Nov. 1997
The manufacture of orthodontic devices and equipment is now a mature industry, and there is an ongoing requirement to provide devices that are efficient, economical and easy to use. Increasingly there is the added requirement for them to be as inexpensive as possible, especially if orthodontists are to be persuaded to make the changes in the procedures in which they were trained, and with which they are very familiar, and that the adoption of any new device usually entails.